EXPOSURE SCHEDULES FOR SUNTANNING PRODUCTS
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EXPOSURE
SCHEDULES FOR
SUNTANNING
PRODUCTS
Application Note: A10 Jan 2022
As part of our policy of continuous product improvement, we reserve the right to change specifications at any time.
It is generally accepted that proper use of indoor tanning methods darkening melanin through oxidation, and building up skin
may be safer for the tanner than the uncontrolled environment thickness (sometimes referred to as the horny layer). It is the
of outdoor tanning. However, it is a common misconception darkening of the melanin (melanogenesis) that we see as
among consumers that indoor tanning is completely safe from tanning.
the harmful effects of UV radiation. Many people mistakenly Burning occurs when the protective process cannot take place
feel comforted when a unit is claimed to be “Food & Drug efficiently enough to offset the UV radiation penetrating the
Administration (FDA) compliant,” because this connotes the skin. The skin becomes red as the capillaries swell in reaction.
idea of a “safe” product. Increased itching and sensitivity now become painful. A time
It is important to realize that compliance merely states that the delay is involved here because, while color is first evident when
product has met certain performance guidelines set forth by the the pink-colored melanin existing in the skin is oxidized to a
FDA/CDRH. In its efforts to regulate the industry, the FDA requires brown color, more melanin is being produced which will later rise
products to meet certain electrical, mechanical, and irradiance to the surface layers to add more color. Thus color and pain from
measurement standards. Suntanning product manufacturers, sunburn often does not occur until much later than the exposure,
in turn, have complied by labeling each product with tanning after significant erythema (skin-pinkening) has already occurred.
schedules and warning labels explaining the hazards involved By understanding the tanning and burning process, we can more
with exposure to UV radiation. easily understand the safety factor involved with the various
Solar radiation (or any light) can be characterized by wavelength, tanning products. Manufacturers can design their products to
the units of wavelength being the nanometer, which is produce light of different spectral characteristics than in the solar
one-millionth of a millimeter. To facilitate the discussion of the radiation of outdoor tanning.
tanning process, we will consider the spectrum of light to be broken For instance, the UVB content of the typical suntanning apparatus
into several groups (see Figure 1) : visible light (400 - 780 nm), varies from less than 0.5 percent to about 4 percent of the total
UVA (320 - 400 nm), UVB (260 - 320 nm) and UVC (200 - 260 nm). output, while the solar spectrum is comprised of approximately
The longer wavelengths penetrate farther into your skin, while the 1 percent to 12 percent of these burning rays. On the other hand,
shorter wavelengths do not reach as deeply. the UVA of tanning units is usually much higher, about 10 times
the radiation from the sun. This control of the spectral output
illustrated one reason why some people believe that indoor
tanning can be considered “safer” than outdoor exposure.
Now, let us put together the two key factors that make up the
idea of “equivalent exposure.” We know that UVB radiation can
be 100 times to 1,000 times more effective in stimulating
erythema than the UVA, and we also know that tanning products
can vary in the amount of the UVA/UVB contained in their output.
It is clear, then, that a unit exposing the skin to high levels of UVB
will produce the tanning effect more quickly than a unit with UVA
concentrated light. This method requires careful attention to
timing, however. The high level of effectiveness of UVB makes a
few minutes of overexposure acutely more harmful that an equal
such overexposure to UVA.
There are two distinct groups of individuals who demand different
performance from tanning products. The first are people who
The visible light has little effect on skin color. The shortest, most
desire to stay in each session as long as possible, either because
dangerous wavelengths of UVC light are absorbed by the earth’s
tanning is a leisurely period of relaxation for them or because
atmosphere outdoors and are filtered or eliminated in indoor
they feel they are getting their money’s worth. The second group
tanning lamps. The UVB is considered to be the burning rays,
doesn’t have time to waste on this sort of thing. They desire to
because these rays are 100 to 1,000 times more effective in
get in and get out as quickly as possible. This group also includes
biologically stimulating the burning process in the skin. The UVA
tanning business owners who, if the tanning sessions are shorter,
radiation reaches deeper layers of the skin, however, and also
serves a role in the oxidative process of tanning.
The burning process to which we refer is called erythema (skin
pinkening) and describes the biological method that protects the
skin from radiation damage. The skin responds to exposure by Application Note: A10 Jan 2022
stimulating melanocyte cell division to produce more melanin, As part of our policy of continuous product improvement,
we reserve the right to change specifications at any time.can schedule more session per day with less apparatus, as well When using phototherapy for treating various skin disorders, the
as saving electricity costs, thus generating higher profit potential. individual’s skin sensitivity can be determined more accurately by
The tanning industry has responded to this dichotomy by creating exposing small areas of previously unirradiated skin with various
lamps with either very low UVB outputs for a “longer” tan, or amounts of UV to ascertain how much irradiation is required to
lamps with higher UVB outputs for a “quicker” tan. Tanning cause erythema. This method is rather impractical for the large
business owners and others would argue that since the amount population of suntanning equipment users, however. In the more
of time is determined by the total effective dose of radiation, practical setting, the individual is usually asked a series of
whether one receives that radiation in 5 minutes or 15 minutes questions to determine his/her skin type.
really doesn’t make much difference because they are “equivalent To derive the maximum exposure times, the spectral irradiance
doses.” All UVA sources emit some UVB to avoid excruciatingly of the unit first must be measured. This is a rather complex and
long exposure times. So, with the longer times required in UVA technical process.
exposure to induce tanning, total exposure to UVB can nearly A spectroradiometer measures the irradiance of the
equal that of tanning with a UVB concentrated source. suntanning unit’s output at each wavelength (see Figure 2). The
The advent of lower UVB output lamps, the differences among spectroradiometer’s calibration is extremely important; it should
tanning unit designs, and the need for a general refining of be calibrated using a known reference light source, and it must
the regulations imposed on the tanning industry prompted the remain stable throughout the measurement. The instrumentation
FDA/CRDH to publish a set of guidelines that manufacturers or must be capable of measuring very small wavelength intervals
importers of suntanning products must meet for any new product over the entire range required. It must have a very narrow
introduced in the United States. (The guidelines became effective bandpass (the number of wavelengths that are allowed to pass
in September 1986.) through the instrument at each measurement point) ; high
Each type of unit introduced must undergo testing, and data wavelength accuracy and precision; extremely low stray light
supporting the calculation of timer settings and tanning schedules levels; and a wide dynamic range (the lowest to highest range
must be submitted to the appropriate agencies before certification of signal of light level that can be measured by an instrument).
can take place. These times are derived from measurements of The instrumentation must be calibrated against NIST (National
the unit’s spectral irradiance (i.e. the lamp’s “power” falling on Institute of Standards and Technology) traceable standards.
a given surface area at a given distance from the source at each Equally as important as using high-caliber measuring
wavelength interval). The spectral irradiance values in Watts/cm2 instrumentation is having the proper training and background
are then modified and used in a formula with the MED factor to necessary to make accurate measurements. Many variables
determine a minimal time of exposure. (MED is the minimal and difficulties that can influence the measurements may be
erythemal dose, or the effective dose, of UV exposure required to encountered. Thus, this type of testing is best performed by a
cause pinkening of the skin.) qualified calibration laboratory experienced in these types of
Two calculations are used to determine the tanning schedules on measurements and utilizing high quality measurement
tanning units. One calculates the maximum recommended time instrumentation.
for a reddening of the skin to occur (Te, or maximum erythemal It is important to note that this instrumentation is not the same
time). The other calculates the maximum recommended time for as the portable, handheld UVA and UVB meters, which are not
a darkening of the skin to occur (Tm, or maximum melanogenic suitable for these types of measurements. The typical, relatively
time). Since different individuals will either tan or burn first, both inexpensive UVA and UVB meters are only practical for monitoring
times are considered, and the shortest one is recommended for the relative reduction in UV intensity of a lamp over time.
deriving tanning schedules. For instance, when the lamp’s output falls to a certain value on
The reaction of Type II individuals is used to decide how the the meter due to aging, a decision can then be made as to when
irradiance values are to be modified. The skin types are rather to replace the lamp. Calibration of these broadband meters is
imprecisely defined for Caucasian skin as being Types I (never typically made at only one wavelength, and inaccuracies of up
tans, always burns) through IV (always tans, hardly ever burns). to 20 percent to 30 percent between identical meters are not
Two other types (V and VI) also exist, but have not typically uncommon. Linearity (the accuracy of response of the instrument
been users of tanning equipment to date. Type I individuals will at various input intensities) is oftentimes assumed or untested.
probably also not be using the product, since they rarely tan; thus, This could result in errors when measuring sources that vary
the required exposure schedules on suntanning equipment are not
directed towards those individuals. Type II is generally used for
calculations, since it is the most sensitive skin type who would
generally use this type of product. Extrapolation of tanning
schedules to other skin types may then be accomplished, if so
Application Note: A10 Jan 2022
desired. As part of our policy of continuous product improvement,
we reserve the right to change specifications at any time.widely in intensity. Thus, while they can provide some useful
relative information, the absolute values obtained from these
types of meters should be treated with caution.
Unfortunately, many users of these meters are not informed
enough to interpret the readings obtained and often draw
incorrect conclusions from them. No spectral information on
the lamps is provided, so attempting to compare lamps that have
significantly different spectral output shapes could be very
misleading. Also, since the tanning effectiveness of different
wavelengths varies widely (according to the action spectrum),
and the meter cannot account for this, no information regarding
a particular lamp’s tanning effectiveness can be assumed, either.
The only valid way to measure a lamp for its absolute
spectral output is with a relatively expensive
spectroradiometer system and trained lab personnel.
Specifically looking at the formula for Te (maximum erythemal
exposure time), we have:
Te (seconds) = 642J / M
2
Σ Vi Ri
where: 642 Joules/M2 = 4x the MED time (where 1 standard MED
equals 156J / M 2 at 296 nm for Type II skin).
Vi = weighting factor from the erythemal action
spectrum for each specific wavelength
Ri = Measured Spectral Irradiance in Watts/M2
(irradiance at each corresponding wavelength)
3 = Summation of weighted values at each wavelength
After the lamp’s spectral intensity is measured, the next task is to To obtain the Te time, one would multiply the measured spectral
determine the effect of this particular tanning unit’s UV irradiance irradiance value at each wavelength by its corresponding
on a person’s skin. This is known as the “effective dose.” weighting factor, then sum all these products {(Vi * Ri ) + (Vi * Ri )
Since not all wavelengths are equally effective at tanning, or ...etc.). Divide this sum into the constant 642J/M2, and this will
at causing erythema, each wavelength can be weighted as to yield the Te time in seconds.
how effective it is, relative to other wavelengths. The weighting The calculation of Tm maximum melanogenic time follows the
factors are determined by the biologically effective action of the same general rules, except that values assigned as the constant
different wavelengths on the Type II individuals, known as the and the spectral weighting factors (derived from a separate action
“action spectrum.” (See Figures 3 and 4.) spectrum) are different.
The erythemal effectiveness of UVB at 296 nm is considered high- 1,836J / M2
Tm (seconds) =
er than any other portion of the spectrum, thus representing the Σ Ji Ri
peak of the action spectrum. All other wavelengths’ effectiveness where: 1,836 Joules/M2 = 4x the MMD (minimal melanogenic
is expressed relative to this maximum value at 296 nm (a process dose) where i standard MMD = 458J/M2 at 296 nm.
known as normalization). Thus, if we apply a given weight from
the action spectrum to each corresponding wavelength measured Ji = weighting factor from the melanogenic action
from the tanning source, we can obtain an effective spectral spectrum for each specific wavelength
irradiance for the source. Ri = same as above
Application Note: A10 Jan 2022
As part of our policy of continuous product improvement,
we reserve the right to change specifications at any time.The manufacturer has the option of developing alternate tanning
schedules for these individuals not to exceed the calculated
maximum timer interval (Te or Tm). These alternate schedules
must be supported by adequately documented test data, reference
to the technical literature, research, or other appropriate
corroborative evidence.
The complications involved with calculating the formulas
mentioned, as well as the extreme accuracy needed to make the
irradiance measurements, are indicative of the importance of
proper procedure when testing tanning devices.
From this brief discussion, it can be seen that the many factors
of UV measurements make the task appropriate only for
experienced laboratory technicians who use highly accurate and
precise instruments. Product manufacturers do well to entrust
their certification testing to a capable lab, and tanning center
operators must protect their own interest by demanding proper
testing and evaluation of exposure schedules.
Whichever value is less between the Te and the Tm time is used
as the maximum exposure limit, or timer interval, for the particular
product. It is typically the Te time that is shorter that the Tm time.
When the maximum exposure time (whether Te or Tm) is
ascertained (and thus the maximum timer setting is also known),
the manufacturer can proceed with creating tanning schedules for
Type II skin, based on the following guidelines:
“The recommended exposure schedule should provide for
exposures of no more than 0.75 MED three times the first week,
gradually increasing the exposure the following weeks until
maximum tanning has occurred (approximately four weeks
total) and then provide for maintenance of a tan by biweekly
or weekly exposures of up to four (4) MEDs or four (4) MMDs,
whichever is less.”
(Aug 4, 1985, publication by the FDA Office of Compliance.)
These calculations do not take into account the effect of certain
medications, disorders, and so forth that may significantly affect a
person’s reaction to UV.
Although using Type II schedule for less sensitive skin types
(i.e. Types III and IV) should prevent any burning, the exposure
schedule may be inadequate to provide tanning, thus, these Application Note: A10 Jan 2022
individuals may not be satisfied with the product’s performance. As part of our policy of continuous product improvement,
we reserve the right to change specifications at any time.
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